Varga Erika, Pusztai Péter, Oszkó Albert, Baán Kornélia, Erdőhelyi András, Kónya Zoltán, Kiss János
Department of Physical Chemistry and Materials Science, ‡Department of Applied and Environmental Chemistry, and §MTA-SZTE Reaction Kinetics and Surface Chemistry Research Group, University of Szeged , H-6720 Szeged, Hungary.
Langmuir. 2016 Mar 22;32(11):2761-70. doi: 10.1021/acs.langmuir.5b04482. Epub 2016 Mar 4.
The effects of reduction by H2 and by heat treatment in vacuum and in O2 flow on Rh particle size changes of Rh/CeO2 samples were studied by X-ray photoelectron spectroscopy (XPS), high-resolution electron microscopy (HRTEM), and CO adsorption followed by diffuse reflectance infrared spectroscopy (DRIFTS). Low-temperature (373-423 K) reduction of Rh without agglomeration is demonstrated. An average particle size of 2.3 ± 1.1 nm was measured by HRTEM regardless of the metal loading (1-5%). On Rh/CeO2, a significant particle size increase of the Rh particles was detected on heating (773 K). In this work, we suggest that the temperature-induced surface decrease resulting from the sintering of Rh is favored only for well-dispersed particles. XP spectra revealed that the mobile oxygens of CeO2 fundamentally determine the oxidation state of the supported metals. At elevated temperature, the oxidation of the reduced support surface as well as the metal component takes place because of the segregation of ceria oxygens. When the aggregated particles were reoxidized, the redispersion of Rh was observed probably because of the formation of Rh-O-Ce bonds.
通过X射线光电子能谱（XPS）、高分辨率电子显微镜（HRTEM）以及CO吸附后进行的漫反射红外光谱（DRIFTS），研究了用H₂还原以及在真空和O₂流中进行热处理对Rh/CeO₂样品中Rh颗粒尺寸变化的影响。结果表明，在低温（373 - 423 K）下Rh能够还原且不会发生团聚。无论金属负载量（1 - 5%）如何，通过HRTEM测得的平均颗粒尺寸为2.3 ± 1.1 nm。对于Rh/CeO₂，在加热（773 K）时检测到Rh颗粒的尺寸显著增大。在这项工作中，我们认为由Rh烧结导致的温度诱导表面减小仅有利于分散良好的颗粒。XP光谱表明，CeO₂的可移动氧从根本上决定了负载金属的氧化态。在高温下，由于二氧化铈氧的偏析，还原后的载体表面以及金属组分都会发生氧化。当团聚颗粒被重新氧化时，可能由于Rh - O - Ce键的形成而观察到Rh的再分散。
